168 



and vice versd. The question then becomes, to determine the acce- 

 leration of angular velocity due to the motion of the system. This 

 is obtained by determining the acceleration of angular momentum 

 for a line fixed in the body, which is then shown to be a maximum 

 for the normal to the plane containing the axes of angular momentum 

 and velocity ; then the acceleration along this line is the total acce- 

 leration of angular momentum due to the motion, and the accelera- 

 tion of angular velocity determined from it (just as the angular velo- 

 city is determined from the momentum) is that due to the motion 

 of the system. Also the acceleration of angular velocity due to the 

 forces is related to the resultant couple and its axis, just as the an- 

 gular velocity to the angular momentum. Thus the accelerations 

 of angular velocity due both to the motion and to the forces being 

 determined, the intensity and direction of the angular velocity at any 

 time is to be found by combining these effects by integration. The 

 problem is worked out in the case of the axis of the resultant couple 

 being coincident with that of angular momentum, so that this remains 

 fixed. The paper concludes with a simple solution of the problems 

 of Foucault's gyroscope as applied to show the effects of the earth's 

 rotation, the simplicity arising from the method of this paper enabling 

 us at once to refer the motion to those axes (neither fixed in the 

 body nor in space) whose motion it is desired to determine. 



March 10, 1856. 



A paper was read by L. Barrett, Esq., " On the Distribution of the 

 Mollusca on the Coast of Norway." (Vide Annals of Nat. Hist. 

 May 1856.) 



In this the author observed, that when the fauna of the coast of Nor- 

 way is compared with that of the other side of the North Atlantic, a 

 great difference will at once be perceived, not only in the number of 

 species, but also in the different distribution of northern and south- 

 ern types ; the Mollusca of Greenland being peculiarly arctic, those 

 of Scandinavia a mixture of southern and northern species. In the 

 southern part of Norway we find the species living on our coasts 

 abundant ; but they become rarer as we go north, their place being 

 supplied by arctic forms. Many of the northern species have a great 

 geographical range, at which we need not be surprised when we 

 consider their great antiquity, many of them having existed since the 

 pliocene period ; and, in the author's opinion, whenever we find a 

 species with a great geographical range, we may at once infer that 

 it has continued to live from a remote period. It is extremely diffi- 

 cult, according to the present state of the currents in the northern 

 seas, to account for the wide distribution of arctic shells on this side 

 of the North Atlantic ; but when we consider that at not a very 

 distant period the temperature and other conditions of this area 

 were totally different, that a cold climate prevailed, certainly accom- 

 panied by a current setting from the north (as is fully proved by the 



